For many years the cartridge syringe has been used by dentists, physicians, veterinarians, and other related medical personnel. These syringes are characterized by a sterilisable tubular component into which a disposable unit dose medication vial can be inserted. A disposable needle mounted on a hub is screwed onto or into the front of the syringe so that the distal portion of the needle penetrates into the cartridge forming a fluid sealing engagement with the cartridge, and a partial opening by way of the cannula. The syringe is equipped with a plunger for expressing the contents of the cartridge through the cannula and into the patient.
Health professionals are becoming increasingly aware of the risks associated with use of the cartridge syringe. These risks include the possibility of physical injury by an inadvertent needle puncture and the more serious threat of cross-contamination and ensuing infection from an inadvertent "needle-stick" injury.
Contracting a serious or deadly disease such as ACQUIRED IMMUNE DEFICIENCY SYNDROME (A.I.D.S.) or Hepatitis B from a contaminated cartridge syringe needle is a very real possibility for healthcare workers. After penetration of an infected patient the cannula of the cartridge syringe is contaminated by the blood of the patient. When the syringe is removed from the patient it becomes an immediate source of infection which must be disposed of very carefully. It poses a serious threat to any individual who may come in contact with it.
Over the years healthcare workers have become more aware of the dangers associated with the cartridge syringe and a number of strategies have evolved to deal with the risks. Needle covers which fit over the cannulas have been used on dental cartridge syringes for many years to prevent needle-stick injuries. These covers or "caps" are removable parts of the needle hub and are inserted onto the front and rear aspects of the hub by the manufacturer prior to shipping. In use at the clinical site the dentist (or hygienist depending on state regulations) inserts an anesthetic cartridge into a dental syringe, removes the rear cap of a dental needle, screws the needle onto the front of a dental syringe, removes the front cap, and then proceeds with the dental injection. After the dental syringe is withdrawn from the mouth the operator may replace the front cap back onto the dental needle until the contaminated needle is either reused on the same patient, or disposed of.
The problem with this technique is that the practice of recapping the dental needle actually increases the risk of an inadvertent "needle-stick" injury since the operator's hands and fingers must come into close proximity with the contaminated cannula as they recap the needle.
"Recapping" the used dental needle is a usual practice in dentistry even though it has been discouraged by many public and private healthcare organizations. Recapping is still commonly practiced by dentists, physicians, and other health care personnel because in order to remove the needle from a reusable cartridge syringe it must be unscrewed from the very same threads to which it was initially screwed onto.
To avoid manual recapping but still permit the use of screw-on cartridge syringe needles some dental product manufacturers have developed dental needle receptacles. These receptacles give the operator of the dental syringe a margin of safety by increasing the operator's physical distance from the contaminated cannula during recapping or unscrewing procedures. They also typically provide a barrier around the receptacle so that hands and fingers will not slip and contact the needle when it is being removed from the syringe. One such recapping system is the "On Guard" system distributed by the Henry Schien Dental Supply Company of Port Washington, N.Y. The problem with this kind of recapping system is that it is unaesthetic, cumbersome, harder to use than it appears, and adds yet another element to the already overcrowded inventory of dental devices. In addition to the above mentioned drawbacks of recapping systems they have one other serious flaw; they are inconvenient to use.
Another method of improving the safety of the common cartridge syringe is to use a disposable unit dose syringe. In this case the needle, cartridge, and barrel are all disposed of together. This method of syringe use is costly, inconvenient, and creates a much larger volume of hazardous waste than traditional methods. It also allows the possibility of reuse by unauthorized persons since the elements of the syringe are all disposed of together in a bulk quantity.
Yet another method designed to improve the safety of the cartridge syringe involves using a needle cutting system which cuts off the cannula at the dental needle hub allowing it to fall into a protected container. This system is inconvenient in practice and may not be much safer since the cut surface of the needle that remains attached to the cartridge syringe is still sharp and possibly infectious. In use the needle hub with its cut end must still be removed from the syringe in the same manner as present art allows; by unscrewing it.
Turning now to patented prior art, a number of individuals have tried to deal with the risks of needle-stick injury and cross-contamination.
U.S. Pat. No. 3,648,695 to Bowen (1972) discloses a pressurized applicator for foamed medications which has an ejecting tip. This device cannot be used to aspirate fluids making it impossible to load medicines from dispensing vials, to draw blood or bodily fluids, or to aspirate as a precautionary action to determine the anatomical location of the cannula tip relative to venous and arterial structures.
The barrel of the pressurized applicator and its corresponding applicator tip are designed for foam applications and will not provide an adequate seal for fluids having low viscosities. Additionally, the high cost of manufacture severely limits the use of this device for routine delivery of medication.
U.S. Pat. No. 4,931,040 to Haber et al. (1990) shows a method by which the cannula bearing section of the syringe can be retracted within a cartridge. The major drawback of this design is that the cartridge and cannula must be manufactured as an integral part thereby complicating the process of manufacture and greatly increasing the cost of the device. This device permits only one use of the cannula prior to disposal even though multiple injections using more than one cartridge are typical. The cumbersome syringe must then be manipulated to retract the cannula.
U.S. Pat. No. 4,932,940 to Walker et al. (1990) shows a retractable needle guard for use with hypodermic syringes. Use of this device requires the operator to retract the guard by hand prior to giving an injection, to inject the patient while the guard is retracted by the surrounding tissues, or to manipulate the device in a manner that causes retraction of the guard just prior to injection. The disadvantage of this device with respect to the disclosed invention is that it does not apply to use of a cartridge type syringe. It also does not provide for convenient cannula disposal or separation of the infectious component from the syringe.
U.S. Pat. No. 4,950,253 to Jacobs shows a needle ejector structure which can be placed into a dental syringe after use to eject the needle hub from the front of the syringe. This device has some limited practicality but requires considerable manipulation of the syringe in order to eject the used needle hub. The act of removing the used anesthetic cartridge and placing the ejector into the barrel of the syringe adds risk to the operator since manipulation of the syringe near the cannula is necessary.
U.S. Pat. No. 4,986,811 to Thead et al. shows an apparatus for removing needles from syringes. This device is designed to unscrew a needle from a syringe. The major drawbacks to this device are that it is relatively expensive to produce and it adds a cumbersome machine component to the already crowded medical inventory. U.S. Pat. No. 4,986,812 to Perler (1991) shows a disposable syringe with a locking device to prevent reuse. It does not relate to convenient and safe disposal of the infectious cannula after use.
Unlike the above described prior art, the invention disclosed herein relates to safe, expeditious, convenient, and economical disposal of the cartridge syringe cannula without requiring the operator to risk injury by recapping or otherwise placing bodily parts near the contaminated cannula.